The purpose of this project is to determine 1) if previous evoked potential predictors of clinical improvement in hyperactive children treated with methylphenidate (Ritalin) can be replicated using current diagnostic quidelines and objective indices of improvement, 2) how Ritalin dosage affects these predictors, 3) what relative contributions habituation and directed attention make to evoked potential predictors, 4) how other psychophysiological measures are related to the AEP, and if they play a contributory role in mediating drug response in this population. These findings will help us develop a model of stimulant drug action in hyperkinetic children. As a secondary goal in the process of testing children, we will determine if a new measure of EEG asymmetry, cortical coupling, is related to academic retardation. Visual evoked potentials, heart rate, and reaction time are recorded from hyperactive children under 4 dosages of Ritalin: (.16 mg/kg, .33 mg/kg, .66 mg/kg and placebo). At the completion of the laboratory sessions, the children are placed on 3 one month cycles of each of the active dosages. A placebo week is randomly inserted into each active medication period. Teachers and parents ratings using double blind controls and known drug sensitive scales are obtained continuously during the clinical trials. Changes in ratings from pre-drug baselines and between placebo and active drug weeks, are used to index behavioral changes associated with drug treatment. Additionally, blind ratings made by the pediatrician are used to index gross clinical changes. Data from the clinical trials and the psychophysiological battery are used to test the specific objectives outlined above.